SEATTLE--After three years of observations using the 10-meter Keck II telescope in Hawaii, Lowell Observatory astronomer Lisa Prato announces discovery of four new low-mass double star systems with separations similar to the Earth-Sun distance or smaller. This survey also serendipitously revealed five new wider binaries with separations of about 14 to 140 times the Earth-Sun distance. The results provide significant new evidence to better characterize the star and planet forming region in Ophiuchus.

"These very closely spaced young, low-mass star pairs are really exciting," said Prato, summarizing results of her study presented today at the American Astronomical Society meeting in Seattle. "We can accurately measure the mass ratios and ultimately the component masses of these pairs, along with their abundance and other properties. These measurements give us new information about star and planet formation in regions just now being probed at this level of detail and resolution."

This research features the first such analysis for young, low-mass spectroscopic (closely spaced) binary stars undertaken in infrared light. The four new spectroscopic binary stars were previously unknown. One of these new pairs is located in a complex and intriguing hierarchical quadruple star system. The study comprised a sample of 33 young M stars -- the coolest, lowest mass class of stars -- in the Ophiuchus molecular cloud and used the Keck II 10-meter telescope atop the 13,796-foot summit of Mauna Kea in Hawaii. The stars in the survey program are approximately 450 light-years distant with an estimated mass range of between 0.3 to 0.7 solar masses.

The study shows that because the size of a habitable zone around low-mass stars corresponds to the typical distance between the stars in spectroscopic binary pairs, the prevalence and properties of such binary star systems have important consequences for potential terrestrial planet formation. "These close, or 'spectroscopic binaries' have separations that are similar to the Earth-Sun separation or even less," said Prato. "This raises the question about what do these systems do to local planet formation? It might be possible to have planets very far away orbiting both stars. On the other hand, if the spectroscopic binary is spaced widely enough, could planets possibly form close to one star? In any case, all this complexity throws a wrench in the works, thus making it even more important to know how many of these systems are out there in the nearby star and planet forming regions like Ophiuchus."

For this survey, the large aperture Keck telescope was equipped on the many nights necessary to observe such a large sample size with the facility's infrared NIRSPEC spectrometer. Because M stars emit most of their light in the infrared, using NIRSPEC on Keck allowed Prato to study these faint targets with optimal facilities. Also, young stars still embedded within this fascinating star and planet forming region are more readily detectable in infrared light because dust blocks most visible light. "It is simply most efficient to search in infrared light wavelengths for young M star spectroscopic binaries with a large aperture telescope such as Keck," said Prato. Together with colleague Michal Simon (Stony Brook University), Prato pioneered the powerful application of infrared spectroscopy to the study of close binary systems.

The paper, "A Survey for Young Spectroscopic Binary K7--M4 Stars in Ophiuchus," has been accepted for publication by the Astrophysical Journal (http://arxiv.org/pdf/astro-ph/0611636). Lisa Prato is the sole author. The research goal was to find young M star spectroscopic binaries in the target region by searching for variability in radial velocity and to measure the mass ratios of any new systems discovered. Mass ratios of the spectroscopic binary stars are determined by the Doppler shift, that is by measuring the spectral signatures, indicating radial velocities, of both components in the spectroscopic binary pairs. Prato discovered two double-lined spectroscopic binary systems, two single-lined systems, and one radial velocity variable.

The occurrence of the young, low-mass, spectroscopic binary star pairs discovered in the study is about 12 percent; this compares closely with other research programs that have measured the abundance of nearby older star spectroscopic binaries, as well as studies to measure the number of higher mass young spectroscopic binary stars in various star forming regions.

"My research so far leads me to suspect that there are more young, low-mass spectroscopic binary stars in Ophiuchus and other star forming regions awaiting discovery," Prato said. "These young, exceptionally small separation binary stars orbiting each other in such close proximity, possibly interacting with dust and gas distributed throughout the systems, will help to determine the potential for planet formation in habitable zones. Young spectroscopic binaries also provide a unique opportunity to measure very accurate stellar mass ratios and eventually stellar masses information that helps astronomers to broadly understand star formation and evolution."

Prato plans to further explore this rich and diverse sample of stars to study circumstellar dust, rotational velocities, and the wide binary properties in future research. Hubble Space Telescope or adaptive optics observations may detect even more wide binaries. Also, a more dense sampling is needed to determine the orbital properties of the newly discovered spectroscopic binaries.

This research was supported by NSF and awards from NASA's Keck PI Data Analysis Fund. Data for this project were obtained at the W.M. Keck Observatory from telescope time allocated to NASA through the agency's scientific partnership with the California Institute of Technology and the University of California.

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About Lowell Observatory

Lowell Observatory is a private, non-profit research institution founded in 1894 by Percival Lowell. The Observatory has been the site of many important findings including the discovery of the large recessional velocities of galaxies by Vesto Slipher in 1912-1914 (a result that led ultimately to the realization the universe is expanding), and the discovery of Pluto by Clyde Tombaugh in 1930. Today, Lowell's 19 astronomers use ground-based telescopes around the world, telescopes in space, and NASA planetary spacecraft to conduct research in diverse areas of astronomy and planetary science. Lowell Observatory currently has four research telescopes at its Anderson Mesa dark sky site east of Flagstaff, Arizona, and is building a 4-meter class research telescope, the Discovery Channel Telescope, in partnership with Discovery Communications, Inc.

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